Inkjet printing is a non-impact method for producing images by the deposition of ink droplets in a pixel-by-pixel manner onto an image-recording element in response to digital signals. There are various methods that may be utilized to control the deposition of ink droplets on the receiver member to yield the desired image. In one process, known as drop-on-demand inkjet printing, individual droplets are ejected as needed onto the recording medium to form the desired image. Common methods of controlling the ejection of ink droplets in drop-on-demand printing include piezoelectric transducers and thermal bubble formation using heated actuators. With regard to heated actuators, a heater placed at a convenient location within the nozzle or at the nozzle opening heats ink in the nozzle to form a vapor bubble that causes a drop to be ejected to the recording medium in accordance with image data. With respect to piezoelectric actuators, piezoelectric material is used in conjunction with each nozzle and this material possesses the property such that an electrical field when applied thereto induces mechanical stresses therein causing a drop to be selectively ejected from the nozzle selected for actuation. The image data provides signals to the printhead determining which of the nozzles are to be selected for ejecting an ink drop, such that each nozzle ejects an ink drop at a specific pixel location on a receiver sheet.
After the ink drop is ejected onto the printing material, it must be dried but that creates numerous problems. Ink that is used for printing with an ink jet is a very thin liquid and contains, for example, a relatively high percentage of water, for example 95%. Therefore, when printing, a very high proportion of moisture is applied to the printing material, this moisture being absorbed by the printing material only with difficulty and only up to a certain limit, before said material ultimately will even tear. Roughly speaking, this absorption limit decreases as the quality and the price of the printing material decrease. Therefore, high-quality and expensive printing materials are particularly suitable in ink-jet printing, for example, printing materials having surface coatings. In particular, in commercially operated roll printing machines, which print, for example, up to 200 running meters of printing material per minute using an ink-jet process, such an expensive printing material frequently represents too high a cost factor for the operator or for the customer.
Additionally, it is possible a customer may want to use a number of different specific printing materials to achieve a particular effect, such as those that can be used in an offset printing process which due to the above described problems might not be suitable for the inkjet printing process. If such a printing material, which cannot absorb enough moisture, is to be used, the moisture applied during the printing process must necessarily be reduced; this means, that also a lower quantity of dye must be used, because, for example, the ratio of water to dye must remain constant at 95% in order to maintain processability in an ink-jet printhead. Therefore, only the overall amount of ink for an individual print job can be reduced; however, this automatically leads to a loss of quality of the printed image, because only a lower color density can be achieved, and thus the color in the printed image remains paler. This is a particularly critical problem in multi-color printing, where sufficient color density should be achieved for each color separation, but where, for this reason, the limit of moisture saturation of the printing material used is reached particularly rapidly.
This device and related method is directed to solving this problem of drying an ink drop while still maintaining the desired color density and quality by using the microwave heating element described below.